Technical Field
The invention relates to an integrated circuit, and particularly relates to an integrated circuit capable of preventing a signal voltage from flowing back to a system voltage rail.
Related Art
Along with development of technology, process technology of integrated circuit (IC) is accordingly improved. As known by those familiar with the IC technology, various electronic circuits can be integrated to/formed on a chip. In order to facilitate communicating (for example, exchanging data) with other external circuits/chips, a pad is configured on the chip.
For example, FIG. 1 is a block schematic diagram of an electronic system having a plurality of ICs. An IC 50 includes a core circuit 51, an impedance matching component 53 and a pad Tx0. A communication terminal of the core circuit 51 can output a data signal to a communication channel 10 through the pad Tx0. A first terminal and a second terminal of the impedance matching component 53 are respectively coupled to a system voltage rail VCC and the pad Tx0. The IC 50 can perform impedance matching to a transmitting terminal of the communication channel 10 by using the impedance matching component 53. An IC 100 includes an impedance matching component 105, a core circuit 110 and a pad Rx0. A communication terminal of the core circuit 110 can receive the data signal from the communication channel 10 through the pad Rx0. A first terminal and a second terminal of the impedance matching component 105 are respectively coupled to a system voltage rail TVCC and the pad Rx0. The IC 100 can perform impedance matching to a receiving terminal of the communication channel 10 by using the impedance matching component 105.
FIG. 2 is a schematic diagram of a backflow path when a signal voltage of the IC 100 of FIG. 1 flows back to the system voltage rail. Referring to FIG. 2, the communication terminal of the core circuit 110 and the first terminal of the impedance matching component 105 are coupled to the pad Rx0. A first terminal and a second terminal of a switch P1 are respectively coupled to the system voltage rail TVCC and a second terminal of the impedance matching component 105. Under a normal operation mode, based on a turn-on state of the switch P1, the impedance matching component 105 can selectively provide a resistance value to the pad Rx0. Therefore, the IC 100 can perform impedance matching to the receiving terminal of the communication channel 10 by using the impedance matching component 105.
When the IC 100 enters a power-off mode (a power-saving mode), a voltage source (not shown) stops supplying power to the system voltage rail TVCC of the IC 100, so as to save a power consumption of the core circuit 110. However, during the period that the IC 100 enters the power-off mode, the IC 50 probably transmits a communication signal to other ICs (not shown) by using the communication channel 10, such that a voltage signal is appeared on the pad Rx0 of the IC 100. During the period that the IC 100 enters the power-off mode, a control signal ZB of the switch P1 probably has an uncertain state (for example, a floating state) or a grounding state, such that the switch P1 cannot be completely turned off (it is assumed that the switch P1 is a P-channel metal oxide semiconductor (PMOS) transistor). Therefore, when a high level (for example, 3.3 V) voltage signal is appeared on the pad Rx0, the voltage signal can flow back to the system voltage rail TVCC through the impedance matching component 105 and the switch P1. The backflow path is shown by an arrow of FIG. 2. The voltage signal flowing back to the system voltage rail TVCC probably causes a wrong operation of the core circuit 110.
FIG. 3 is a schematic diagram of another backflow path when a signal voltage of the IC 100 of FIG. 1 flows back to the system voltage rail. It is assumed that the switch P1 is a PMOS transistor, so that a junction between a second terminal (a drain) of the switch P1 and a body (or bulk) of the switch P1 forms a parasitic diode D. The body of the switch P1 is coupled to the system voltage rail TVCC. During the period that the IC 100 enters the power-off mode, when a high level (for example, 3.3 V) voltage signal is appeared on the pad Rx0, the voltage signal can flow back to the system voltage rail TVCC through the impedance matching component 105 and the parasitic diode D of the switch P1. The backflow path is shown by an arrow of FIG. 3. Therefore, the voltage signal backflow phenomenon may cause a voltage increase of the system voltage rail TVCC, and accordingly causes a wrong operation of the core circuit 110.